1. Field of the Invention
The present invention concerns torsional damper devices of the kind comprising at least two coaxial parts disposed to rotate relative to one another within the limits of a defined sector of relative angular displacement and against the action of damper means.
2. Description of the Prior Art
As is known, in the case, for example, of a friction disk for a clutch, as for an automobile vehicle, for example, this rotation is further counteracted by circumferentially acting elastic means such as coil springs.
In practice the damper means principally consist in friction means comprising one or more spring loaded friction rings. A torsional damper of this kind is described, for example, in French patent application No. 2 494 795 published on May 28, 1982; in this instance one of the coaxial parts comprises two guide rings whereas the other comprises a flange disposed between these rings.
There are also known torsional damper devices in which a part of the friction means operates with variable hysteresis, which means that they are operative only beyond a minimum relative angular displacement. An example is given in U.S. Pat. No. 4,398,625 of Aug. 6, 1983.
It has been realized that although such torsional damper devices comprise parts suitable for diverse applications, such as the flange and the guide rings, for example, the same does not apply in the case of the friction means since these provide only for obtaining one value of spring loading of the friction rings which form part of them.
A principle objective of the invention is to provide for obtaining a number of levels of spring loading of the friction rings which form part of this kind of friction means.